Studies in humans and experimental animals suggest that nutritional deficiencies influence the immune response following vaccination. Conversely, living vaccines may adversely affect the nutritional status of the host. In many human populations, dietary deficiencies of protein and energy are usually accompanied by deficiencies in trace minerals such as zinc. The objectives of this investigation are (a) to study the influence of protein and zinc deficiencies, singly and combined, on the efficacy of Bacille Calmette-Guerin (BCG) vaccination in guinea pigs and (b) to determine the effect of vaccination infection on selected parameters of growth and metabolism of protein and/or zinc deficient guinea pigs. The response to vaccination will be monitored by measuring the growth and dissemination of BCG organisms in vivo, the delayed hypersensitivity response to skin test with purified protein derivative (PPD), and the blastogenic response of peripheral blood leukocytes in vitro. The efficacy of vaccination will be determined by respiratory challenge with attenuated mycobacteria. The impact of diet and infection on the nutritional status of the guinea pigs will be evaluated by measuring changes in body weight, food consumption, hemoglobin, white cell count, total serum proteins, albumin, transferrin, plasma zinc, copper and iron, and two important zinc-dependent enzymes in leukocytes, alkaline phosphatase and superoxide dismutase.